The 2-wire method is commonly used as it is the simplest and most straightforward method. In 2-wire, you can get accurate measurements above 100 kΩ relatively easily. For precision measurements with resistances (ohms) below 100 kΩ, 4-wire works more reliably and conveniently than 2-wire. 4-wire requires 4-wire switching and more cabling. You may decide the tradeoff is acceptable, depending on the accuracy versus complexity requirements of your system.
The following figure shows a 4-wire resistance (ohms) measurement, including lead and switching resistance:

Current (amps) is forced through the source leads (HI, LO). As a result, a voltage develops across the resistance (ohms) under test. By measuring the voltage directly across the resistor using the sense leads, the voltage drop of interconnects (RLEAD) is ignored.

It doesn't matter. However, we suggest that you may fix screws for the better measurement. The metal flakes with the screws connect to the chasses ground; as a result, fix screws could reduce the environmental noise and statics.

The USB supports up to 127 different devices. Additional USB devices are connected through hubs in a tiered star topology which consists of multiple USB peripherals connected to a single USB hub and multiple USB hubs connected in a chain, one to another.

M3500-opt01 Multi-point Scanner Card is not allowed of direct current measurements; however, on-card shunt resistors can be installed for channels 1 and 6 to allow for indirect current measurements. The figures below show the typical configuration for current measurements.

The current through each shunt resistor can be calculated as follows:

I= current being determined

V= voltage measured by multimeter

R= shunt resistance value

Instead of manually calculating current, set up a MX+B math calculation function. (M=1/R and B= 0.). The M3500A will then display the actual current value.

Note: If there are two devices under test, the value of User-installed Shunts(R) have to be the same.

M3500A supports 7 types of Thermocouple: E, J, K, N, R, S and T. Via thermocouple adapter, user must measure a known temperature junction (T1) and then modulate the value of reference junction according to the result. The value of reference Junction must be stable, so that user can measure an accurate temperature.

How to modulate the value of reference junction for thermocouple measurement:

1. Configure the thermocouple type and unit. Pressing CONFIG >> SHIFT >> TEMP(TCOUPL), and then using PREV and NEXT to select the type and unit.
2. Measure a known temperature junction (T1). The result of the measurement is Tm.
3. Modulate M3500A reference junction to make Tm=T1.
Reference junction modulation：
Panel:
CONFIG >> SHIFT >> TEMP(TCOUPL) >> NEXT >> NEXT >> SIMULATE >> ENTER
Pressing 「PREV」 or 「 NEXT」 and 「RANGE」 to modulate the reference junction.
PC remote control Command:
「:TCO:RJUN：Sim value」
Example:
If the reference junction=23.0°C, T1=30°C，Tm=25°C, we should modulate the reference junction to 28.0°C to make Tm=30°C. ?

USBTMC stands for USB Test &Measurement Class. Any USB device conforms to USBTMC without the limitations of operation systems and environment can work under VISA assistance, and communicate with a computer. In other words, The control procedures via VISA to USBTMC device and via VISA to GPIB device are the same.
USBTMC is a protocol built on top of USB. Any USB device conforms to USBTMC can work under VISA assistance without the limitations of operation systems and environment, and communicate with a computer.Via USBTMC and USB488 protocol the USB device behaviors just like a GPIB device, and the GPIB commands can be compliant to the USB software. The advantage of using USBTMC is that you don't have to insert any card in the PC, including GPIB card. And also you don't have to re-program the previous application software which is for GPIB. Only the instrument conforms to USBTMC protocol in the VISA basis, and the version of NI-VISA 3.2 or later is installed in the PC. The USBTMC unit will be recognized, and can be used.
Just like our multimeter M3500A. M3500A USB interface conforms to USBTMC protocol completely.Via a standard built-in USB interface, the M3500A can simulate the GPIB interface, and get up to the same function. To download NI driver, please click into NI website

After setting up our application software, PT-TOOL & PT-LINK, or your own programs, the M3500A will be easy to control.
It is important to note that not all USB devices support USBTMC. The device maker has to add the USBTMC support in the device firmware. Please refer to the instrument's documentation, and check whether it is USBTMC compliant.
In the following are the command examples of USBTMC and GPIB. The main different areas will be marked in red. It's obvious that the program codes are almost the same.

Please set trigger time by pressing the buttons on the front panel.
MENU -> NEXT to TRIG -> ENTER -> NEXT to DELAY -> ENTER. The problem is regarding the time setting
of trigger delay. Then, please in the PT-TOOL software input the remote control command for speeding up
the scan capability. "TRIG:DELAY 0.1".

Please do the warm-up step in two hours for solution. Because the temperature of the instrument
and the adapter must be the same so that measuring the value will be stable. To do the warm-up step can
let the instrument and the adapter with the same temperature.

Please confirm the version of NI visa is 3.1 or upward. If it is incorrect, please refer to our User
guide in CD we enclosed with the Instrument to link the NI website and download the correct NI Visa
to operate.

【Step 1】When use the M3500A Digital Multimeter and Power Supply as substitute for the Source meter to measure IV Curve, you will use thecurrent measurement function in M3500A. Connect the M3500A between the Power Supply and PV Module as shown in Figure 1. Then, convert the voltage value of Power supply and the current value of M3500A to IV Curve. However, the differences due to Multimeter Burden Voltage will occur when using this measurement. To eliminate this measurement differences, we can use the M3500A with Scanner card to do the Multi-point Voltage measurement as shown in Figure 2.

Figure 1

【Step 2】Connect one known resistance R_shunt between the PV Module and Power Supply. When current pass the R_shunt, it will generate thevoltage VR_shunt.
Scanner card CH1 measure the voltage of PV Module.
Scanner card CH2 measure the voltage of VR_shunt.
Then, we can calculate the Current (I) = VR_shunt/R_shunt
This measurement can reduce the differences from Burden Voltage and measure the IV Curve accurately